Polysaccharide aldehydes prepared by oxidation method and used as strength additives in papermaking

Abstract

Polysaccharide aldehydes are prepared using selective oxidation involving the use of nitroxyl radical mediated aqueous oxidation with a limited amount of oxidant and defined reaction conditions. These polysaccharide aldehyde derivatives having maximum effective aldehyde and minimal carboxylic acid levels making them especially useful as wet, temporary wet and dry strength additives for paper.

What is claimed is:  
     
       1. A method for preparing polysaccharide aldehyde derivatives having maximum effective aldehyde content comprising oxidizing polysaccharide in an aqueous solution with an oxidant having an equivalent oxidizing power of up to 14.18 g of active chlorine per mole of polysaccharide anhydrosugar unit (“ASU”) and an effective mediating amount of nitroxyl radical, the reaction being carried out at a temperature of at or less than about 15° C. and a pH of from about 8.0 to 10.5, the resulting product having up to 15 mole % of C-6 aldehyde groups per mole of polysaccharide ASU and aldehyde to carboxylic acid ratios of greater than or equal to 0.5 based on moles of polysaccharide ASU of each functionality. 
     
     
       2. The method of  claim 1  for preparing polysaccharide aldehyde derivatives wherein the polysaccharide aldehyde derivatives are starch aldehyde derivatives and the polysaccharide is starch. 
     
     
       3. The method of  claim 1  wherein the nitroxyl radical catalyst has the formula:                    
       where Y is H, OH or NH—C(O)—CH 3  and each of the R groups represent the same or different alkyl groups of 1 to 18 carbon atoms. 
     
     
       4. The method of  claim 3 , wherein Y is selected from the group consisting of H and NH—C(O)—CH 3 . 
     
     
       5. The method of  claim 1  wherein the oxidant has an equivalent oxidizing power of from about 0.35 to 14.18 g of active chlorine per mole of polysaccharide ASU. 
     
     
       6. The method of  claim 5  wherein the oxidant is sodium hypochlorite or sodium hypobromite. 
     
     
       7. The method of  claim 1  wherein the oxidant is sodium hypochorite or sodium hypobromite and the resulting product has from about 1 to 15 mole % of aldehyde groups per mole of polysaccharide ASU and from about 0 to 20 mole % of carboxylic acid content per mole of polysaccharide ASU. 
     
     
       8. The method of  claim 1  wherein from about 5 to 20 mole % of oxidant is used, the reaction temperature is from about 5 to 10° C., and the pH is from about 9 to 10. 
     
     
       9. The method of  claim 1  wherein the polysaccharide is modified with a cationic group. 
     
     
       10. The method of  claim 1  wherein the oxidation is carried out in slurry reaction. 
     
     
       11. The method of  claim 1  wherein the oxidation is carried out in a slurry reaction, from about 5 to 20 mole % of oxidant is used, the reaction temperature is from about 5 to 10° C. and the pH is from about 9 to 10. 
     
     
       12. The method of  claim 1  wherein the oxidation is carried out in a slurry reaction, from about 5 to 20 mole % of oxidant is used, the reaction temperature is from about 5 to 10° C., the pH is from about 9 to 10, the polysaccharide is modified with a cationic group, and the resulting product has from about 1 to 7 mole % of aldehyde groups per mole of polysaccharide ASU. 
     
     
       13. The method of  claim 1  wherein the oxidation is carried out in a dispersed state, from about 5 to 20 mole % of oxidant is used, the reaction temperature is from about 5 to 10° C., the polysaccharide is modified with a cationic group, and the pH is from about 9 to 10. 
     
     
       14. The method of  claim 1  wherein the oxidant is hypobromite formed in situ by the addition of sodium bromide and sodium hypochlorite. 
     
     
       15. The polysaccharide aldehyde derivative produced by the method of  claim 1 . 
     
     
       16. The polysaccharide aldehyde derivative of  claim 15  wherein the polysaccharide aldehyde derivatives are starch aldehyde derivatives and the polysaccharide is starch. 
     
     
       17. The polysaccharide aldehyde derivative produced by the method of  claim 5 . 
     
     
       18. The polysaccharide aldehyde derivative of  claim 17  wherein the polysaccharide aldehyde derivatives are starch aldehyde derivatives and the polysaccharide is starch.